There exists a need in the marketplace to store/retrieve large amounts of data/information in a compact volume while making the data/information readily available. A particularly challenging application for a data storage systems is in use with compact data processing systems. The volume and orientation allowed for a storage system depends upon the space available inside or adjacent to the data processing system. For example, UNIX based processing systems often provide a rack in which a data storage systems can be horizontally mounted. Data storage systems are often positioned vertically adjacent to personal computer based processing systems to minimize the floor/desk area occupied by the storage system.
One type of storage system that can store/retrieve large amounts of data includes a plurality of data cartridges (e.g. tape cartridge/cassettes or disks) which are stored in an array of storage slots, a data read/write device (e.g. tape drive or disk drive), and a transport device. Data is stored on the data cartridges. When data is to be transferred from/to the storage system, a data cartridge is moved by the transport device from a storage slot to the data read/write device which transfers the desired data. After completion of the data transfer, the transport device returns the data cartridge to a storage slot.
The storage capacity of a storage system can be increased by increasing the number of storage slots and the corresponding number of data cartridges. The time required to store/retrieve data (i.e. data access time) can be decreased by utilizing multiple data read/write devices thereby providing simultaneous access to several data cartridges within the storage system.
Some known storage systems arrange the storage slots in a linear or a circular array. For linear storage arrays, the data read/write device(s) is generally placed adjacent to and aligned with an end of the storage array so that the transport device can travel along a linear path and face the openings of the storage slots and the read/write device. A limitation of a linear arrangement of the storage array and the read/write device(s) is the relatively large size of the storage system and the slow data access times for data cartridges which are distant from the read/write device.
For circular arrays, the data read/write device is generally interposed between storage slots and the transport device is placed near the center of the circular array so that the transport device can rotate and access the openings of the storage slots and the data read/write device.
A limitation of these types of storage systems is that the read/write device physically occupies space that would otherwise be available for use as storage slots, thereby decreasing the storage capacity of the storage system. An increase in the number of data read/write devices requires a substantial decrease in storage capacity and/or-a substantial increase in the physical volume of the storage system. Some storage systems compensate for this loss of storage slots by increasing the volume of the storage array such as by increasing the width/diameter of the arrangement of storage slots or by utilizing two dimensional stacking (e.g. a box arrangement or a cylindrical arrangement) of the storage slots. The large volume, small storage capacity, and/or slow data access times of these known storage systems precludes their use in many applications, such as with some compact data processing systems.
Many storage devices can operate in substantially one predetermined orientation. For example, some storage systems utilize gravity to retain the data cartridges in the storage slots by tilting the insertion/removal end of the slot upward. Such storage systems are limited to an orientation in which the weight of the data cartridges retains them in the slots. Other storage systems utilize a storage array that rotates in a substantially horizontal plane about an axis to position a storage slot adjacent to the transport device. If the storage array is oriented so that the data cartridges are rotated along a different plane, a number of problems are encountered, especially if there is an uneven distribution of data cartridges in the array. For example, a varying amount of power is needed to accelerate/decelerate the storage array into a selected position which, in turn, increases the complexity .of accurately controlling movement of the storage array. Furthermore, vibrational problems are generated by such a rotating storage array.